US20220152535A1 - Melt-blown depth filter element and method of making it - Google Patents
Melt-blown depth filter element and method of making it Download PDFInfo
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- US20220152535A1 US20220152535A1 US17/587,519 US202217587519A US2022152535A1 US 20220152535 A1 US20220152535 A1 US 20220152535A1 US 202217587519 A US202217587519 A US 202217587519A US 2022152535 A1 US2022152535 A1 US 2022152535A1
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Images
Classifications
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- B01D39/14—Other self-supporting filtering material ; Other filtering material
- B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
- B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D—SEPARATION
- B01D39/00—Filtering material for liquid or gaseous fluids
- B01D39/14—Other self-supporting filtering material ; Other filtering material
- B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
- B01D39/1607—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous
- B01D39/1623—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres the material being fibrous of synthetic origin
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
- B01D2239/0604—Arrangement of the fibres in the filtering material
- B01D2239/0622—Melt-blown
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
- B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
- B01D2239/065—More than one layer present in the filtering material
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- B—PERFORMING OPERATIONS; TRANSPORTING
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Definitions
- This specification relates to depth filter elements, to melt blown media and to methods of making them.
- a depth filter retains particles throughout the depth of a filtration media.
- Various media can be used to construct a depth filter, one of them being a non-woven media of melt blown or spun bond filaments.
- a depth filter may have multiple layers (or zones), with the layer having the largest pore size usually forming an upstream layer and the layer having the smallest pore size usually forming a downstream layer. This is in contrast to surface filters, alternatively called screen filters, which retain particles primarily by size exclusion on or near an upstream separation layer rather than throughout the depth of the filtration media.
- a surface filter may provide some depth filtration for particles below its rated absolute particle size, but the amount of depth filtration is limited by the surface filter's lack of thickness and the desire to make any layers behind the upstream separation layer as permeable as possible.
- a depth filter may be distinguished from a surface filter by way of the depth filter's substantial thickness, which is typically at least 5 mm and more often at least 10 mm.
- a depth filter is also typically provided in a configuration that provides a smooth inner and outer peripheral surface to maximize its volume whereas a surface filter is typically folded or pleated so as to maximize its surface area.
- a cartridge filter installation has one or more removable or replaceable cartridges placed in a housing.
- a typical cartridge has a filter element with end caps or other fixtures adapted to connect the cartridge to the housing. Some cartridges may be cleaned, but they are typically discarded at the end of their useful life.
- a depth filter element may be rated according to its dirt holding capacity (DHC), which is measured by weight of solid particles that the filter can hold before plugging.
- DHC dirt holding capacity
- the useful life of an element is measured as the time the element can be operated under specified conditions before reaching a specified maximum pressure drop across the depth filter cartridge.
- the useful life of an element may be limited by its DHC or by its mechanical ability to withstand the applied pressure as it becomes loaded with particles.
- Other rating criteria include the efficiency of the element in removing particles of a specified size and the clean water pressure drop of the element. For example, a removal efficiency rating may be specified as 90% removal of particles down to a specified micron size or as “absolute” (meaning 99%) removal of particles down to a specified micro
- U.S. Pat. No. 6,986,427 issued on Jan. 17, 2006 to Aune et al., describes a melt blown non-woven media useful for a depth filter element.
- the media is made by directing a plurality of melt blown filaments at the side of a conical end of a tubular structure.
- the tubular structure rotates on a spinning mandrel.
- the tubular structure grows in length as material is added to its conical end while the tubular structure is drawn out of the filament spray area along the length of the mandrel.
- Different filaments are directed at different portions of the cone, and the filaments may vary in one or more characteristics along the length of the cone. This produces concentric annular zones in the tubular element with a corresponding variation in the one or more characteristics.
- One or more other melt blown filaments may be applied across the length of the cone to add filaments that extend through the depth of the element, crossing multiple zones, to strengthen the media.
- U.S. Pat. No. 6,938,781 which shares a common priority application with U.S. Pat. No. 6,986,427, describes a non-woven depth filter element that includes a cylindrical mass of essentially continuous melt-blown polymer filaments and an essentially continuous traversing melt blown polymer filament extending through the mass.
- the cylindrical mass has a depth dimension, a longitudinal dimension, and a circumferential dimension.
- the filaments of the cylindrical mass are generally oriented in the longitudinal and circumferential dimensions and form a plurality of concentric zones.
- the traversing filament extends in the longitudinal dimension through a substantial portion of a length of the cylindrical mass while extending around the cylindrical mass in the circumferential dimension and extending radially in the depth dimension through substantially an entire thickness of two or more zones of the cylindrical mass.
- Polypropylene depth filter elements made according to the patents described above are sold by GE Water and Process Technologies in association with the Z.PLEX trade mark. These elements have inside diameters of about 1 inch (25 mm) and outside diameters of about 2 inches (51 mm) to 2.75 inches (70 mm). They are used in a number of water filtration applications.
- This specification describes a depth filter element having one or more, preferably three or more, concentric zones. Each zone includes an essentially continuous melt blown filament. An additional filament reciprocates through the depth of the element. The additional filament defines a helicoid of varying diameter. The mass of the traversing filament is preferably biased towards one or more outer concentric zones.
- This specification also describes a method of making a depth filter element.
- Melt blown filaments are sprayed onto a rotating mandrel.
- One set of filaments is sprayed from one or more nozzles that are fixed in place relative to the mandrel.
- Another filament is sprayed from a nozzle assembly that moves laterally or has compound motion relative to the mandrel.
- the nozzle assembly oscillates relative to the mandrel while part of the nozzle assembly oscillates relative to the remainder of the nozzle assembly.
- the frequency of oscillation relative to the mandrel is preferably less than the frequency of oscillation relative to the nozzle assembly.
- Lateral movement of the nozzle assembly relative to the mandrel produces a spray pattern than traverses at least part of the depth of the element.
- Compound motion produces a spray pattern that traverses part of the depth of the element in a single oscillation but traverses more, preferably all, of the depth of the element over multiple oscillations.
- a traversing filament is produced from a nozzle assembly that translates back and forth relative to a mandrel.
- An attenuator of the nozzle assembly oscillates relative to the remainder of the nozzle assembly.
- the nozzle assembly preferably dwells at an end of its translation.
- FIG. 1 is a photograph of a depth filter cartridge taken from its right side.
- FIG. 2 is a photograph of the depth filter cartridge of FIG. 1 taken from its left side.
- FIG. 3 is a schematic end view of the depth filter cartridge of FIG. 1 as it is being formed.
- FIG. 4 is a schematic drawing of a machine for making the depth filter cartridge of FIG. 1 .
- Approximating language may be applied to modify any quantity that could vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms such as “about” is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Range limitations may be combined and/or interchanged, and such ranges, and all sub-ranges, are included herein unless context or language indicates otherwise. Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of materials, process conditions and the like, used in the specification and the claims, are to be understood as modified in all instances by the term “about”.
- Optional or “preferable” and similar terms mean that the subsequently described event or circumstance may or may not occur, or that the subsequently identified material may or may not be present, and that the description includes instances where the event or circumstance occurs or where the material is present, and instances where the event or circumstance does not occur or the material is not present.
- the term “may” is used to indicate conditions that might or might not be present.
- the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion.
- a process, method, article or apparatus that comprises a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such process, method article or apparatus.
- the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.
- a depth filter element described herein provides a useful alternative to existing filter elements.
- the depth filter element may have, for example, an outside diameter of at least 2.0 inches (25 mm), optionally at least 4.5 inches (114 mm).
- An exemplary filter element is made with a melt blown traversing filament sprayed onto a filter element as it is being formed on a rotating mandrel.
- the traversing filament is produced with an air-attenuated nozzle that disperses the filament within a cone shaped spray area.
- the attenuator pivots such that the cone shaped spray area oscillates across part of the length the filter being formed.
- the nozzle also reciprocates from side to side relative to the length of the mandrel to further expand the distance covered by the spray area.
- the reciprocating nozzle is believed to place more traversing filament mass towards the outside of the filter element. This effect can be enhanced by reciprocating the nozzle such that it spends a disproportionate amount of time at or near the side of its travel corresponding to the outside of the element.
- an oscillating but laterally fixed traversing filament spray pattern tends to provide sub-optimal traversing filament mass in the outer zones of a filter. This becomes more noticeable in filter elements with large diameters and thick walls. Moving the traversing filament nozzle laterally relative to the mandrel while forming the filter allows for relatively more of the mass of the traversing filament to be located in an outer zone or zones. This is believed to stiffen the structure of the outer zone or zones of the filter and help prevent open voids from collapsing in these zones.
- a low frequency lateral oscillation of the nozzle relative to the mandrel itself also appears to have beneficial effects on the lifetime and dirt holding capacity of the element. This oscillation could also be biased towards the inner diameter zones in the instance of an inside to outside flow condition.
- a depth filter cartridge 10 has a tubular depth filter element 12 , a left side end cap 14 and a right side end cap 16 .
- the words “left side” and “right side” are arbitrary and will be used in this description merely to provide a means to describe the cartridge 10 as it is oriented in the figures.
- the cartridge 10 or a part of it, may also be described as having length (measured in a longitudinal dimension parallel to a line between the left and rights sides of the cartridge), circumference (measured in a circumferential dimension along a circle perpendicular to the longitudinal dimension), or depth (measured in a radial dimension perpendicular to the circumferential dimension).
- the end caps 14 , 16 may be made of a thermoplastic material and are preferably thermally bonded to each end of the depth filter element 12 to form a seal with the ends of the depth filter element 12 .
- the end caps 14 , 16 may be bonded to the depth filter element 12 by an adhesive or by other means known in the art.
- the end caps 14 , 16 fluidly separate the outside of the depth filter element 12 from the hollow center of the depth filter element 12 .
- a porous core tube (not visible) extends through the hollow center of the depth filter element 12 and is attached and sealed to the end caps 14 , 16 .
- the depth filter cartridge 10 is typically used after inserting it into a housing or shell, not shown.
- the housing may hold one, or more than one, cartridge 10 .
- feed water to be filtered flows through an inlet into a plenum defined by the inside of the housing and the outside of the cartridge 10 .
- the feed water then flows through the depth filter element 12 and filtered water collects in the hollow center of the depth filter element 12 or the core tube.
- One or both of the end caps 14 , 16 has an opening for the filtered water connected to an outlet of the housing.
- the left side end cap 14 includes an adapter 18 and a seal 20 , which plug into an outlet of the housing.
- the seal 20 is an O-ring located in a groove in the adapter 18 .
- a seal 20 may be formed by potting an elastomeric material in a groove to provide a planar annular gasket around an adapter 18 that is in the form of a simple hole, or by other means known in the art.
- the depth filter cartridge 10 may be used in an inside-out filtration mode by reversing the flows of water described above. In this case, variations in the structure of the element 12 between its inner and outer surfaces are preferably inverted.
- the depth filter element 12 comprises a plurality of media layers or zones 22 through its depth.
- the zones decrease in retention size (particle size removed at a given efficiency) from the outside surface 24 to the inside surface 26 of the depth filter element 12 .
- large particles will be retained near the outside surface 24 and progressively smaller particles will be retained as the feed passes inwards through the depth filter element 12 .
- the zones 22 are illustrated with a sharp line between them for ease of illustration, in practice there may be a more gradual transition, or a transitional area, between zones 22 . Although 5 zones 22 are preferred, as shown, there could be more or less zones. In the depth filter element 12 of FIGS.
- the depth filter element 12 has an outside diameter of about 6.5 inches and an inside diameter of about 3 inches.
- the length of the cartridge 10 is about 38 inches, which corresponds with a nominal length of 40 inches.
- the adapter 18 is a standard type 226 fitting, although other suitable fittings may be used.
- the dimensions of the cartridge 10 may also be varied.
- the outside diameter may be larger or smaller, preferably in the range of 3 inches to 9 inches, or 4.5 inches to 7 inches.
- the length may also be larger or smaller, for example a nominal 60-inch cartridge may be made.
- a surface filter may be provided inside of the depth filter element 12 in the manner described in International Publication Number WO 2012/034028, which is incorporated by reference.
- the surface filter may, for example, rest on a core tube having an outside diameter of between about 1.1 inches and 3 inches and extend to an outside diameter of the inner surface filter of between about 2 inches and 4.5 inches.
- the cartridge 10 of FIGS. 1 and 2 is made with a polypropylene (PP) depth filter element 12 and PP end caps 14 , 16 thermally welded to the depth filter element 12 .
- the end caps 14 , 16 could be made of another polymer, such as ABS, and they could be attached to the element 12 with an adhesive.
- Other materials useful for forming the depth filter element 12 include, for example, other polyolefins such as polyethylene, cellulose, polyamides, polyesters, and mineral fibers. Multiple materials may be used in a single cartridge 10 .
- the depth filter element 12 may be made of melt blown media wherein each zone 22 is a mass formed of one or more essentially continuous polymer filaments. As will be described below in relation to FIG. 4 , each zone 22 is made of polymer supplied from a melt blown filament delivery system. Subject to the possibility of random breaks, each zone 22 is made from a single essentially continuous filament. The filaments making up the zones 22 extend primarily in the longitudinal and circumferential directions. Preferably, the depth filter element 12 also comprises one or more multiple zone filaments 32 .
- the multiple zone filaments 32 are essentially continuous polymer filaments extending in the depth dimension between two or more zones 22 , preferably between all of the zones 22 . In FIG. 3 (and in the cartridge of FIGS. 1 and 2 ) the multiple zone filaments 32 include static filaments 28 and Z-filaments 30 , also called traversing filaments, as described in U.S. Pat. Nos. 6,938,781 and 6,986,427.
- FIG. 3 is an end view of an element 12 as it is being formed.
- filaments making up the zones 22 are built up into a mass layer upon layer by being sprayed from longitudinally spaced positions against a rotating conical end of the depth filter element 12 being formed.
- the end of element 12 is therefore generally conical, but it is actually a helicoid or screw with radial lines in its plane at a shallow angle relative to a longitudinal axis of the element 12 , rather than at a right angle as in a typical screw.
- the multiple zone filaments 32 are similarly sprayed against the rotating end of the depth filter element 12 being formed, but these filaments 32 are sprayed in a pattern that extends longitudinally across multiple zones 22 .
- the multiple zone filaments 32 are thereby placed between successive turns of the helicoids that make up the zones 22 .
- a multiple zone filament 32 is not primarily responsible for forming any particular zone 22 .
- the multiple zone filaments 32 collectively provide less than 50% of the filament mass in any zone.
- the mass of the static filament or filaments 28 is highest, at least on a per unit volume basis but preferably also on an absolute basis, in the innermost zone or zones 22 .
- the diameter of the static filament or filaments 28 may be about the same as or larger than the diameter of the filaments used in the innermost zone 22 .
- a static filament 28 strengthens the inner zones 22 , which would otherwise be weak in compression given the small filament diameter used in the inner zones 22 to provide retention of small particles.
- the Z-filament or filaments 30 are sprayed in a pattern that traverses back and forth across a helix on the helicoidal end of the depth filter element 12 being formed.
- the diameter of this helix oscillates.
- the frequency of this oscillation is highly exaggerated in
- the Z-filament 30 is produced from a delivery system with a compound movement, for example a relatively high frequency oscillation superimposed on a relatively low frequency oscillation.
- the high frequency oscillation is preferably at least 3 times the frequency of rotation of the mandrel.
- the high frequency oscillation is 6 times the frequency of rotation of the mandrel and so 6 large apexes are produced.
- the smaller and even more frequent apexes are a figurative illustration only of the somewhat random pattern produced by air attenuation at the end of the spray nozzle. Referring back to the 6 large apexes, the low frequency oscillations causes the large apexes to move radially outwards and inwards which, considering that FIG.
- the magnitude of the low frequency oscillation may be less than the magnitude of the high frequency oscillation.
- the apparent frequency of the low frequency oscillation is highly exaggerated in FIG. 3 in order to make the resulting movement more visible.
- the low frequency oscillation is one tenth or less of the frequency of rotation of the mandrel.
- the movement of the Z-filament 30 oscillations from near the outside surface 24 , towards the inside surface 26 , and back towards the outside surface 24 may occur over 10 or more layers of the element 12 rather than just one as shown in FIG. 3 .
- the low frequency oscillation may also be irregular, in particular it may be biased towards the outside of the depth filter element 12 .
- the Z-filament 30 provides a filament mass that is concentrated (i.e. it has areas of higher and lower density) in the circumferential direction whereas a static filament 28 and the filaments making up the zones 22 have homogenous density in the circumferential dimension.
- a Z-filament 30 thereby links multiple zones 22 , preferably all of the zones 22 , together with compression resistant regions without greatly increasing the density of the depth filter element 12 as a whole.
- the mass of the Z-filament or filaments 30 is preferably between 2 and 20% of the mass of the depth filter element 12 .
- the per unit volume density of Z-filament 30 may be higher in inner zones 22 to further strength these zones.
- Z-filament 30 may make up about 25% of the filament mass in the innermost zone 22 A and about 5% of the filament mass in the outermost zone 22 E.
- the outermost zone 22 E has more volume than the innermost zone 22 A.
- the mass of Z-filament 30 in the outermost zone 22 E is preferably equal to or higher than the mass of Z-filament 30 in the innermost zone 22 A.
- the depth filter element 12 shown has five zones 22 labeled, from the innermost zone to the outermost zone, as zones 22 A to zone 22 E. These zones 22 may also be referred to as the first to fifth zones 22 respectively.
- the outer or fifth zone 22 E includes a freestanding portion 32 and an overlapping portion 34 .
- the overlapping portion 34 extends through at least 50% of at least one other zone 22 .
- the overlapping portion 34 in FIG. 3 extends across the entire fourth zone 22 D and partially into the third zone 22 C, although it is also possible to have less overlap.
- the freestanding portion 32 may be omitted.
- the last zone is made as described for the fifth zone 22 above.
- a thin layer of bonding fibers is added over the outermost zone 22 as described in U.S. Pat. Nos. 6,938,781 and 6,986,427.
- the bonding fibers reduce the appearance of loose filament loops and provide a protective cage on the outer surface of the depth filter element 12 .
- These bonding fibers may also shrink as they cool, which provides roughness to increase the effective surface area of the depth filter element 12 .
- FIG. 1 While the Figures are directed to cylindrical filters, the same principles may be applied to a flat sheet or planar product.
- a flat product may be produced along a flat table with the filament sprayers oscillating across the width of the table or by cutting a depth filter element made on a large cylindrical mandrel along its length to obtain a sheet of material.
- the system 110 includes motor driven screw type extruder 112 , which is supplied with thermoplastic polymeric material from a source (not shown).
- a source not shown.
- Polypropylene is preferred but other materials such as polyesters, NylonTM, or polyurethanes may also be used for some or all of the filaments.
- the polymeric material is heated to a molten state, at which time it is metered and conveyed into heated delivery lines 114 .
- the material is conveyed to two filament delivery systems 116 and 118 .
- each of these filament delivery systems 116 , 118 could have separate material conveying systems.
- Filament delivery system 116 includes, for each of five nozzles 127 , 128 , 129 , 216 and 217 , a motor driven gear type positive displacement metering pump 120 which receives molten polymeric material from heated delivery line 114 and pumps it to heater block 122 .
- the speed of motor 124 which drives metering pump 120 , and thus the rate at which the material is metered through pump 120 is electronically controlled by an appropriate controller 126 .
- Motor 124 and controller 126 are shown for only nozzle 127 to simplify the figure, but would typically also be provided one for each of nozzles 128 , 129 , 216 and 217 .
- Each heater block 122 which is independently heated via heating means (not shown), is provided with an internal passage that leads to one of nozzles 127 , 128 , 129 , 216 and 217 .
- the heating means and thus the temperature of the polymeric material within heater block 122 , is controlled by temperature control 130 .
- Each nozzle 127 , 128 , 129 , 216 and 217 includes an orifice, the size of which may be selected as desired to assist in achieving a desired filament size or diameter.
- the molten material fed to each nozzle 127 , 128 , 129 , 216 and 217 exits the respective orifice in a stream.
- Attenuating mechanisms 131 , 132 , 133 , 218 and 219 which comprise a plurality of gas or air jets. Gas flowing out of the attenuating mechanisms 131 , 132 , 133 , 218 and 219 functions to attenuate the stream of molten material exiting from nozzles 127 , 128 , 129 , 216 and 217 to form polymeric filaments in a manner known in the art.
- Attenuating mechanisms 131 , 132 , 133 , 218 and 219 accordingly may be of any design known in the art including that described in U.S. Pat. No. 4,173,443 by Lin, the disclosure of which is incorporated herein by reference.
- Attenuating mechanisms 131 , 132 , 133 , 218 and 219 are associated with an optional gas heater 134 and gas supply source 136 .
- Gas supply source 136 provides gas via conduit 138 and appropriate valves and regulators to heater 134 .
- the temperature of heater 134 is elevated or lowered to the desired temperature via temperature control 140 .
- the gas is then fed from heater 134 through conduit 142 to attenuating mechanism 131 .
- Attenuating mechanisms 131 , 132 , 133 , 218 and 219 may be provided with gas from a common supply source or alternatively separately controlled gas sources may be employed for each attenuating mechanism 131 , 132 , 133 , 218 and 219 .
- flow control valves (not shown) are typically provided so that each attenuating mechanism 131 , 132 , 133 , 218 , 219 may receive air at a different rate.
- Filament delivery system 118 is substantially similar to that of system 116 described above, except that filament delivery system 118 delivers a filament so as to actively intermingle with filaments produced by one or more of the nozzles used in system 116 .
- Filament delivery system 118 has a nozzle assembly 117 , which includes a polymer extrusion nozzle 144 , a heater block 146 , and an attenuator 154 .
- Heater block 146 is connected to independently driven positive displacement metering pump 148 and motor 150 .
- Heater block 146 is provided with temperature control 152 . Pressurized gas is passed to attenuating mechanism 154 from gas supply source 156 via conduit 158 .
- filament pattern 221 overlaps with at least half of pattern 220 , optionally at least 85% of pattern 220 or all of pattern 220 , and possibly also part of pattern 170 .
- Filament collection device 174 includes central, rotatable collection device 176 , alternatively called a mandrel, which extends from drive motor 178 .
- Press roller 180 which rotates about axle shaft 181 , is disposed adjacent to mandrel 176 and spaced therefrom. The completed filter element 12 is removed from the open end of collection device 176 , which is not visible but would be at the left side of the collection device 176 shown in FIG. 4 .
- polymer filaments of filament patterns 166 , 168 , 170 , 220 and 221 may be produced by extruding polypropylene heated to a temperature of between about 280 degrees C. and about 400 degrees C. at a rate of about 5 to 20 pounds per hour per nozzle while passing an ambient gas at a temperature of about 25 degrees C. at a rate of about 10 to 20 standard cubic feet per minute over the molten polymer stream exiting the nozzle orifice.
- the mandrel 176 may rotate at between 200 and 600 rpm.
- Compound filament pattern 172 comprises attenuated pattern 172 A, high frequency pattern 172 B and low frequency pattern 172 C.
- Attenuated pattern 172 A is generally conical pattern generated by the somewhat random movement of the filament as it is blown by air jets from the attenuator 154 .
- High frequency pattern 172 B is created by pivoting attenuated pattern 172 A so that is sweeps across a distance of about 50% to 85% of the distance between the primary pattern edges 182 and 184 at the mandrel 176 .
- the entire high frequency pattern 172 B moves from side to side according to low frequency pattern 172 C to create the entire compound filament pattern 172 , which generally covers the entire distance between edges 182 and 184 at the mandrel 176 .
- Servo driven sweep mechanism 198 causes attenuating mechanism 154 to sweep back and forth through an angle so that the attenuated pattern 172 A traverses back and forth along a longitudinal dimension of filament mass 186 according to high frequency pattern 172 B.
- pattern 172 A traverses two or more of fiber patterns 166 , 168 , 170 , 220 and 221 with each sweep, and continues sweeping while reciprocating laterally, it deposits an essentially continuous polymer filament across the overall laydown pattern, which extends between the primary pattern edges 182 and 184
- sweep mechanism 198 comprises a servo drive motor with a cam and follower mechanism.
- Other suitable devices such as AC/DC driven mechanical cranks and push rod mechanisms, for example, are also acceptable.
- sweep mechanism 198 runs at about 800 to 1200 oscillations per minute while the mandrel 176 rotates at 200 to 600, preferably 240 to 400, revolutions per minute (RPM).
- RPM revolutions per minute
- the nozzle assembly 117 When moving between its end points, the nozzle assembly 117 has a generally constant velocity.
- the nozzle assembly 117 may be reciprocated by a servo or other mechanism, and it may have non-linear motion. In another options, the nozzle assembly may swing through an arc rather than moving laterally.
- polymer filaments of compound filament pattern 172 are produced in the depth filter of the instant invention by passing polypropylene heated to a temperature of between about 280 degrees C. and about 400 degrees C. through a nozzle having an orifice size of about 0.016 inch at a rate of about 8 pounds per hour and passing at an ambient gas at a temperature of about 25 degrees C. at a rate of about 7 standard cubic feet per minute over the molten polymer stream exiting the nozzle orifice.
- Other suitable parameter combinations may also be used.
- An accumulated mass of filaments 186 is produced on mandrel 176 .
- press roller 180 is oriented at an angle relative to mandrel 176 with nip 200 in contact with mandrel 176 .
- outer surface 202 of press roller 180 is angularly displaced by about 1 to 10 degrees relative to mandrel 176 .
- nip 200 contacts mandrel 176 close to edge 182 of filament pattern 166 . Because of the angular placement of press roller 180 , compression of filaments in collective filament mass 186 varies along the length of press roller 180 . This results in a filament mass having a varying density gradient in the radial dimension, with the filament density of filament pattern 166 being generally greater than that of the filament masses comprised of outer filament patterns.
- Compound filament pattern 172 combined with the rotation of mandrel 176 , causes the fibers coming from nozzle 144 to integrate into mass 186 as a “z” direction fiber, extending radially through the zones produced by filament patterns 166 , 168 , 170 , 220 and 221 .
- Filament patterns 166 , 168 , 170 , 220 and 221 produce the zones 22 shown in FIG. 3 .
- Z-filament 30 of FIG. 3 is produced by compound filament pattern 172 .
- Z-filament 30 is preferably placed in a continuous manner from the inside to the outside and back to the inside of 2 or more of the zones 22 during approximately 120 degrees or less of rotation of the depth filter element 12 and over all of the zones 22 during approximately 10 or more rotations (3600 degrees or more of rotation) of the depth filter element 12 .
- system 214 includes heater block 230 , independently driven positive displacement metering pump 232 and motor 234 .
- Heater block 230 is provided with nozzle 224 and temperature control 236 .
- System 214 is also provided with attenuating mechanism 226 associated with nozzle 224 . Pressurized gas is passed to attenuating mechanism 226 from gas supply source 238 via conduit 240 .
- attenuators 226 can be associated with an optional gas heater, not shown.
- the provision of separate filament delivery systems 118 and 214 enables separate control and production of polymeric filaments produced by each system 118 and 214 , although each of the filament delivery systems 118 and 214 produces filaments which traverse filament mass 186 in a radial, or z, dimension.
- the source of material for filament delivery system 214 is extruder 112 via delivery line 114 ; in another embodiment, the material source for system 214 is separate to provide alternate materials to those used in filament delivery systems 116 , 118 and 214 .
- Delivery system 214 produces a stream of a discrete, essentially continuous polymer filament that is distributed in flared pattern 228 and directed from nozzle 224 and attenuating mechanism 226 toward filament collection device 174 .
- the filament pattern 228 is directed in a flared pattern toward rotating mandrel 176 .
- filament pattern 228 spans the distance between a far edge 182 of stream 166 and a far edge 184 of stream 221 .
- filament pattern 228 does not span the distance between far edges 182 and 184 , but does cover a significant portion of the forming layers of filament mass 186 , e.g., the distance covered by filament pattern 228 is greater than the distance covered by each primary filament stream 166 , 168 , 170 , 220 and 221 individually. Preferably the distance covered by filament pattern 228 is greater than the distance covered by two or more adjacent primary filament streams 166 , 168 , 170 , 220 and 221 . In one embodiment, nozzle 224 is placed at an acute angle of about 10 degrees to about 20 degrees relative to mandrel 176 . Static filament 28 in FIG. 3 corresponds with the filament of spray pattern 228 .
- Shell-forming filament delivery system 222 is substantially similar to system 116 described above, except that shell-forming filament delivery system 222 is preferably configured and positioned to produce a relatively smooth outer shell zone on the exterior cylindrical surface of filament mass 186 .
- Shell-forming filament delivery system 222 preferably uses a different location, polymer throughput rate, and air attenuation setting relative to filament delivery system 116 .
- nozzle 244 is preferably placed closer to mandrel 176 and uses a lower polymer throughput rate; additionally, attenuating mechanism 246 uses less air attenuation.
- shell-forming filament delivery system 222 includes heater block 248 , metering pump 250 , motor 252 , temperature control 254 , gas supply source 256 , and conduit 258 .
- polymer filaments of filament pattern 262 is produced by extruding polypropylene heated to a temperature of between about 240 degrees C. and about 325 degrees C. through nozzle 244 having an orifice size of about 0.016 inch at a rate of about 1 pound per hour and passing an ambient gas at a temperature of about 25 degrees C. at a rate of about 1.5 standard cubic feet per minute over the molten polymer stream exiting the nozzle orifice.
- Nozzle 244 is preferably placed so that the filament produced thereby is deposited on the outer zone 22 e formed by filament pattern 221 .
- This configuration produces a very shallow zone or shell with significant fiber-to-fiber bonding, including some bonding between the fibers of the shell and the fibers of outer zone 22 e.
- the fiber-to-fiber bonding of the shell essentially eliminates the presence of loose fibers on the surface of the finished depth filter element 12 and significantly increases the surface area of the resulting depth filter element 12 .
- a sample element was made with a Z-filament nozzle assembly having compound motion.
- the element had a 3 inch (76 mm) inside diameter and 6.5 inch (165 mm) outer diameter.
- the element had 5 concentric zones produced by 5 fixed nozzles that collectively produced a 22 inch (560 mm) wide spray pattern.
- the Z-filament nozzle had an attenuator that produced a spray pattern about 10-15 degrees wide.
- the Z-filament attenuator oscillated at a rate of 1200 cycles per minute.
- the mandrel rotated at 400 revolutions per minute.
- the oscillations of the Z-filament attenautor produced a spray pattern that is about 16 inches (410 mm) wide at the mandrel.
- the Z-filament nozzle is mounted to a heater block that is angled towards the free end of the mandrel (to the left in FIG. 4 ) but displaced away from the free end of the mandrel such that the nozzle is still aimed at about the center of the fixed nozzle spray pattern.
- the nozzle assembly reciprocates through a distance of about 6 inches (150 mm) at a rate of about 5.5 to 6 cycles per minute.
- the nozzle assembly dwells for about 1 to 2 seconds at the side of its travel closest to the free end of the mandrel.
- the sample element, with compound nozzle assembly motion, and the alternative elements were tested under essentially identical conditions. There were no visual signs of crushing or other deformation of the element, and no signs of crushing demonstrated by changes in filtrate turbidity, throughout the lifetime of the sample element. However, both of the alternative elements had visual signs of crushing and increased filtrate turbidity towards the ends of their lifetimes.
- the second alternative element, with nozzle assembly translation only had a lifetime 55% as long as the sample element, and 75% of the dirt holding capacity of the sample element.
- two smaller sample elements were made with a Z-filament nozzle assembly having compound motion. These elements had a 1 inch (25 mm) inside diameter and 2.5 inch (64 mm) outer diameter. The elements had 4 concentric zones produced by 4 fixed nozzles.
- An alternative element of the same inside and outside diameter and total filament mass was made by oscillating the Z-filament attenuator but without reciprocating the Z-filament nozzle assembly.
- the sample elements made with compound nozzle assembly motion and the alternative elements were tested under essentially identical conditions. The alternative element has a lifetime of 61 minutes.
Abstract
Description
- This application is divisional of U.S. application Ser. No. 15/549,446, filed Aug. 8, 2017, which is a National Stage Entry of International Application No. PCT/US2016/025758, filed Apr. 1, 2016, which is a non-provisional application of U.S. application Ser. No. 62/153,641, filed Apr. 28, 2015. U.S. application Ser. No. 15/549,446 and 62/153,641 and International Application No. PCT/US2016/025758 are incorporated by reference.
- This specification relates to depth filter elements, to melt blown media and to methods of making them.
- The following background discussion is not an admission that anything discussed below is common general knowledge or citable prior art.
- A depth filter retains particles throughout the depth of a filtration media. Various media can be used to construct a depth filter, one of them being a non-woven media of melt blown or spun bond filaments. A depth filter may have multiple layers (or zones), with the layer having the largest pore size usually forming an upstream layer and the layer having the smallest pore size usually forming a downstream layer. This is in contrast to surface filters, alternatively called screen filters, which retain particles primarily by size exclusion on or near an upstream separation layer rather than throughout the depth of the filtration media. A surface filter may provide some depth filtration for particles below its rated absolute particle size, but the amount of depth filtration is limited by the surface filter's lack of thickness and the desire to make any layers behind the upstream separation layer as permeable as possible. A depth filter may be distinguished from a surface filter by way of the depth filter's substantial thickness, which is typically at least 5 mm and more often at least 10 mm. A depth filter is also typically provided in a configuration that provides a smooth inner and outer peripheral surface to maximize its volume whereas a surface filter is typically folded or pleated so as to maximize its surface area.
- A cartridge filter installation has one or more removable or replaceable cartridges placed in a housing. A typical cartridge has a filter element with end caps or other fixtures adapted to connect the cartridge to the housing. Some cartridges may be cleaned, but they are typically discarded at the end of their useful life. A depth filter element may be rated according to its dirt holding capacity (DHC), which is measured by weight of solid particles that the filter can hold before plugging. The useful life of an element is measured as the time the element can be operated under specified conditions before reaching a specified maximum pressure drop across the depth filter cartridge. The useful life of an element may be limited by its DHC or by its mechanical ability to withstand the applied pressure as it becomes loaded with particles. Other rating criteria include the efficiency of the element in removing particles of a specified size and the clean water pressure drop of the element. For example, a removal efficiency rating may be specified as 90% removal of particles down to a specified micron size or as “absolute” (meaning 99%) removal of particles down to a specified micron size.
- U.S. Pat. No. 6,986,427, issued on Jan. 17, 2006 to Aune et al., describes a melt blown non-woven media useful for a depth filter element. The media is made by directing a plurality of melt blown filaments at the side of a conical end of a tubular structure. The tubular structure rotates on a spinning mandrel. The tubular structure grows in length as material is added to its conical end while the tubular structure is drawn out of the filament spray area along the length of the mandrel. Different filaments are directed at different portions of the cone, and the filaments may vary in one or more characteristics along the length of the cone. This produces concentric annular zones in the tubular element with a corresponding variation in the one or more characteristics. One or more other melt blown filaments may be applied across the length of the cone to add filaments that extend through the depth of the element, crossing multiple zones, to strengthen the media.
- U.S. Pat. No. 6,938,781, which shares a common priority application with U.S. Pat. No. 6,986,427, describes a non-woven depth filter element that includes a cylindrical mass of essentially continuous melt-blown polymer filaments and an essentially continuous traversing melt blown polymer filament extending through the mass. The cylindrical mass has a depth dimension, a longitudinal dimension, and a circumferential dimension. The filaments of the cylindrical mass are generally oriented in the longitudinal and circumferential dimensions and form a plurality of concentric zones. The traversing filament extends in the longitudinal dimension through a substantial portion of a length of the cylindrical mass while extending around the cylindrical mass in the circumferential dimension and extending radially in the depth dimension through substantially an entire thickness of two or more zones of the cylindrical mass.
- Polypropylene depth filter elements made according to the patents described above are sold by GE Water and Process Technologies in association with the Z.PLEX trade mark. These elements have inside diameters of about 1 inch (25 mm) and outside diameters of about 2 inches (51 mm) to 2.75 inches (70 mm). They are used in a number of water filtration applications.
- International Application No. PCT/US2014/064125, filed by General Electric Company on Nov. 5, 2014, describes another depth filter element. One of the filaments in this element is formed in a spray pattern that is angled towards an adjacent spray pattern so as to overlap with at least 50% of the adjacent spray pattern. These filters may be made in a larger format, for example with inside diameters of about 3 inches (76 mm) and outside diameters of about 6.5 inches (165 mm).
- The following introduction is intended to introduce the reader to the detailed description to follow and not to limit or define the claimed invention. A claimed invention may be a sub-combination of elements or steps described below, or include an element or step described in other parts of this specification.
- This specification describes a depth filter element having one or more, preferably three or more, concentric zones. Each zone includes an essentially continuous melt blown filament. An additional filament reciprocates through the depth of the element. The additional filament defines a helicoid of varying diameter. The mass of the traversing filament is preferably biased towards one or more outer concentric zones.
- This specification also describes a method of making a depth filter element. Melt blown filaments are sprayed onto a rotating mandrel. One set of filaments is sprayed from one or more nozzles that are fixed in place relative to the mandrel. Another filament is sprayed from a nozzle assembly that moves laterally or has compound motion relative to the mandrel. In an example of compound motion, the nozzle assembly oscillates relative to the mandrel while part of the nozzle assembly oscillates relative to the remainder of the nozzle assembly. The frequency of oscillation relative to the mandrel is preferably less than the frequency of oscillation relative to the nozzle assembly. Lateral movement of the nozzle assembly relative to the mandrel produces a spray pattern than traverses at least part of the depth of the element. Compound motion produces a spray pattern that traverses part of the depth of the element in a single oscillation but traverses more, preferably all, of the depth of the element over multiple oscillations.
- In an example, a traversing filament is produced from a nozzle assembly that translates back and forth relative to a mandrel. An attenuator of the nozzle assembly oscillates relative to the remainder of the nozzle assembly. The nozzle assembly preferably dwells at an end of its translation.
-
FIG. 1 is a photograph of a depth filter cartridge taken from its right side. -
FIG. 2 is a photograph of the depth filter cartridge ofFIG. 1 taken from its left side. -
FIG. 3 is a schematic end view of the depth filter cartridge ofFIG. 1 as it is being formed. -
FIG. 4 is a schematic drawing of a machine for making the depth filter cartridge ofFIG. 1 . - Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantity that could vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms such as “about” is not limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Range limitations may be combined and/or interchanged, and such ranges, and all sub-ranges, are included herein unless context or language indicates otherwise. Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of materials, process conditions and the like, used in the specification and the claims, are to be understood as modified in all instances by the term “about”.
- “Optional” or “preferable” and similar terms mean that the subsequently described event or circumstance may or may not occur, or that the subsequently identified material may or may not be present, and that the description includes instances where the event or circumstance occurs or where the material is present, and instances where the event or circumstance does not occur or the material is not present. The term “may” is used to indicate conditions that might or might not be present.
- As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article or apparatus that comprises a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such process, method article or apparatus. The singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.
- A depth filter element described herein provides a useful alternative to existing filter elements. The depth filter element may have, for example, an outside diameter of at least 2.0 inches (25 mm), optionally at least 4.5 inches (114 mm). An exemplary filter element is made with a melt blown traversing filament sprayed onto a filter element as it is being formed on a rotating mandrel. The traversing filament is produced with an air-attenuated nozzle that disperses the filament within a cone shaped spray area. The attenuator pivots such that the cone shaped spray area oscillates across part of the length the filter being formed. The nozzle also reciprocates from side to side relative to the length of the mandrel to further expand the distance covered by the spray area. Relative to a polymer nozzle and attenuator adapted to oscillate through a wider arc to cover a similar distance, the reciprocating nozzle is believed to place more traversing filament mass towards the outside of the filter element. This effect can be enhanced by reciprocating the nozzle such that it spends a disproportionate amount of time at or near the side of its travel corresponding to the outside of the element.
- Without intending to be limited by theory, the inventors believe that an oscillating but laterally fixed traversing filament spray pattern tends to provide sub-optimal traversing filament mass in the outer zones of a filter. This becomes more noticeable in filter elements with large diameters and thick walls. Moving the traversing filament nozzle laterally relative to the mandrel while forming the filter allows for relatively more of the mass of the traversing filament to be located in an outer zone or zones. This is believed to stiffen the structure of the outer zone or zones of the filter and help prevent open voids from collapsing in these zones. A low frequency lateral oscillation of the nozzle relative to the mandrel itself also appears to have beneficial effects on the lifetime and dirt holding capacity of the element. This oscillation could also be biased towards the inner diameter zones in the instance of an inside to outside flow condition.
- Referring to
FIGS. 1 and 2 , adepth filter cartridge 10 has a tubulardepth filter element 12, a leftside end cap 14 and a rightside end cap 16. The words “left side” and “right side” are arbitrary and will be used in this description merely to provide a means to describe thecartridge 10 as it is oriented in the figures. Thecartridge 10, or a part of it, may also be described as having length (measured in a longitudinal dimension parallel to a line between the left and rights sides of the cartridge), circumference (measured in a circumferential dimension along a circle perpendicular to the longitudinal dimension), or depth (measured in a radial dimension perpendicular to the circumferential dimension). - The end caps 14, 16 may be made of a thermoplastic material and are preferably thermally bonded to each end of the
depth filter element 12 to form a seal with the ends of thedepth filter element 12. Alternatively, the end caps 14, 16 may be bonded to thedepth filter element 12 by an adhesive or by other means known in the art. The end caps 14, 16 fluidly separate the outside of thedepth filter element 12 from the hollow center of thedepth filter element 12. Preferably, a porous core tube (not visible) extends through the hollow center of thedepth filter element 12 and is attached and sealed to the end caps 14, 16. - The
depth filter cartridge 10 is typically used after inserting it into a housing or shell, not shown. The housing may hold one, or more than one,cartridge 10. In an outside-in filtration mode, feed water to be filtered flows through an inlet into a plenum defined by the inside of the housing and the outside of thecartridge 10. The feed water then flows through thedepth filter element 12 and filtered water collects in the hollow center of thedepth filter element 12 or the core tube. One or both of the end caps 14, 16 has an opening for the filtered water connected to an outlet of the housing. In thecartridge 10 shown, the leftside end cap 14 includes anadapter 18 and aseal 20, which plug into an outlet of the housing. Theseal 20 is an O-ring located in a groove in theadapter 18. Alternatively, aseal 20 may be formed by potting an elastomeric material in a groove to provide a planar annular gasket around anadapter 18 that is in the form of a simple hole, or by other means known in the art. Alternatively, thedepth filter cartridge 10 may be used in an inside-out filtration mode by reversing the flows of water described above. In this case, variations in the structure of theelement 12 between its inner and outer surfaces are preferably inverted. - Referring to
FIG. 3 , thedepth filter element 12 comprises a plurality of media layers or zones 22 through its depth. Preferably, the zones decrease in retention size (particle size removed at a given efficiency) from theoutside surface 24 to theinside surface 26 of thedepth filter element 12. Thus, large particles will be retained near theoutside surface 24 and progressively smaller particles will be retained as the feed passes inwards through thedepth filter element 12. Although the zones 22 are illustrated with a sharp line between them for ease of illustration, in practice there may be a more gradual transition, or a transitional area, between zones 22. Although 5 zones 22 are preferred, as shown, there could be more or less zones. In thedepth filter element 12 ofFIGS. 1 and 2 , each of its five zones 22 has a different filament diameter and retention size with both the filament diameter and retention size decreasing towards theinside surface 26. Optionally two or more zones 22 may have the same filament diameter or retention size, but preferably while still providing an overall decrease in retention size towards theinside surface 26 for thedepth filter element 12 as a whole. - In the example of
FIGS. 1 and 2 , thedepth filter element 12 has an outside diameter of about 6.5 inches and an inside diameter of about 3 inches. The length of thecartridge 10 is about 38 inches, which corresponds with a nominal length of 40 inches. Theadapter 18 is astandard type 226 fitting, although other suitable fittings may be used. The dimensions of thecartridge 10 may also be varied. For example, the outside diameter may be larger or smaller, preferably in the range of 3 inches to 9 inches, or 4.5 inches to 7 inches. The length may also be larger or smaller, for example a nominal 60-inch cartridge may be made. Optionally, a surface filter may be provided inside of thedepth filter element 12 in the manner described in International Publication Number WO 2012/034028, which is incorporated by reference. In this case, the surface filter may, for example, rest on a core tube having an outside diameter of between about 1.1 inches and 3 inches and extend to an outside diameter of the inner surface filter of between about 2 inches and 4.5 inches. - The
cartridge 10 ofFIGS. 1 and 2 is made with a polypropylene (PP)depth filter element 12 and PP end caps 14, 16 thermally welded to thedepth filter element 12. In other options, the end caps 14, 16 could be made of another polymer, such as ABS, and they could be attached to theelement 12 with an adhesive. Other materials useful for forming thedepth filter element 12 include, for example, other polyolefins such as polyethylene, cellulose, polyamides, polyesters, and mineral fibers. Multiple materials may be used in asingle cartridge 10. - The
depth filter element 12 may be made of melt blown media wherein each zone 22 is a mass formed of one or more essentially continuous polymer filaments. As will be described below in relation toFIG. 4 , each zone 22 is made of polymer supplied from a melt blown filament delivery system. Subject to the possibility of random breaks, each zone 22 is made from a single essentially continuous filament. The filaments making up the zones 22 extend primarily in the longitudinal and circumferential directions. Preferably, thedepth filter element 12 also comprises one or more multiple zone filaments 32. The multiple zone filaments 32 are essentially continuous polymer filaments extending in the depth dimension between two or more zones 22, preferably between all of the zones 22. InFIG. 3 (and in the cartridge ofFIGS. 1 and 2 ) the multiple zone filaments 32 include static filaments 28 and Z-filaments 30, also called traversing filaments, as described in U.S. Pat. Nos. 6,938,781 and 6,986,427. -
FIG. 3 is an end view of anelement 12 as it is being formed. As will be described further in relation toFIG. 4 , filaments making up the zones 22 are built up into a mass layer upon layer by being sprayed from longitudinally spaced positions against a rotating conical end of thedepth filter element 12 being formed. As theelement 12 is rotated, new layers of filaments are pressed against the existing layers at pressroll contact line 11. The end ofelement 12 is therefore generally conical, but it is actually a helicoid or screw with radial lines in its plane at a shallow angle relative to a longitudinal axis of theelement 12, rather than at a right angle as in a typical screw. The multiple zone filaments 32 are similarly sprayed against the rotating end of thedepth filter element 12 being formed, but these filaments 32 are sprayed in a pattern that extends longitudinally across multiple zones 22. The multiple zone filaments 32 are thereby placed between successive turns of the helicoids that make up the zones 22. A multiple zone filament 32 is not primarily responsible for forming any particular zone 22. The multiple zone filaments 32 collectively provide less than 50% of the filament mass in any zone. - The multiple zone filaments 32, among other things, improve fiber to fiber bonding and provide an interlocking element to the mechanical structure of the other filaments. Without intending to be limited by theory, the multiple zone filaments 32 may function to loft the layers of filament within the zones 22 to thereby increase the void volume of the
element 12. The multiple zone filaments 32 are placed between layers of filament within the zones 22 and may also thereby help prevent the zones 22 from collapsing. - The mass of the static filament or filaments 28 is highest, at least on a per unit volume basis but preferably also on an absolute basis, in the innermost zone or zones 22. The diameter of the static filament or filaments 28 may be about the same as or larger than the diameter of the filaments used in the innermost zone 22. A static filament 28 strengthens the inner zones 22, which would otherwise be weak in compression given the small filament diameter used in the inner zones 22 to provide retention of small particles.
- The Z-filament or
filaments 30 are sprayed in a pattern that traverses back and forth across a helix on the helicoidal end of thedepth filter element 12 being formed. The diameter of this helix oscillates. The frequency of this oscillation is highly exaggerated in -
FIG. 3 for the purposes of illustration. The Z-filament 30 is produced from a delivery system with a compound movement, for example a relatively high frequency oscillation superimposed on a relatively low frequency oscillation. The high frequency oscillation is preferably at least 3 times the frequency of rotation of the mandrel. In the example shown, the high frequency oscillation is 6 times the frequency of rotation of the mandrel and so 6 large apexes are produced. The smaller and even more frequent apexes are a figurative illustration only of the somewhat random pattern produced by air attenuation at the end of the spray nozzle. Referring back to the 6 large apexes, the low frequency oscillations causes the large apexes to move radially outwards and inwards which, considering thatFIG. 3 is an end view of a cone or helicoid, means that the large apexes are also moving longitudinally from one apex to another. As indicated inFIG. 3 , the magnitude of the low frequency oscillation may be less than the magnitude of the high frequency oscillation. However, the apparent frequency of the low frequency oscillation is highly exaggerated inFIG. 3 in order to make the resulting movement more visible. Preferably, the low frequency oscillation is one tenth or less of the frequency of rotation of the mandrel. In other words, the movement of the Z-filament 30 oscillations from near theoutside surface 24, towards theinside surface 26, and back towards theoutside surface 24 may occur over 10 or more layers of theelement 12 rather than just one as shown inFIG. 3 . The low frequency oscillation may also be irregular, in particular it may be biased towards the outside of thedepth filter element 12. - The Z-
filament 30 provides a filament mass that is concentrated (i.e. it has areas of higher and lower density) in the circumferential direction whereas a static filament 28 and the filaments making up the zones 22 have homogenous density in the circumferential dimension. A Z-filament 30 thereby links multiple zones 22, preferably all of the zones 22, together with compression resistant regions without greatly increasing the density of thedepth filter element 12 as a whole. The mass of the Z-filament orfilaments 30 is preferably between 2 and 20% of the mass of thedepth filter element 12. Optionally, the per unit volume density of Z-filament 30 may be higher in inner zones 22 to further strength these zones. For example, Z-filament 30 may make up about 25% of the filament mass in the innermost zone 22A and about 5% of the filament mass in theoutermost zone 22E. However, assuming equal zone thickness, theoutermost zone 22E has more volume than the innermost zone 22A. To prevent outer zone collapse, particular inelements 12 with an outside diameter of 4.5 inches (114 mm) or more used with an outside-in flow path, the mass of Z-filament 30 in theoutermost zone 22E is preferably equal to or higher than the mass of Z-filament 30 in the innermost zone 22A. - As shown in
FIG. 3 , thedepth filter element 12 shown has five zones 22 labeled, from the innermost zone to the outermost zone, as zones 22A to zone 22E. These zones 22 may also be referred to as the first to fifth zones 22 respectively. The outer orfifth zone 22E includes a freestanding portion 32 and an overlappingportion 34. The overlappingportion 34 extends through at least 50% of at least one other zone 22. For example, the overlappingportion 34 inFIG. 3 extends across the entire fourth zone 22D and partially into thethird zone 22C, although it is also possible to have less overlap. Optionally, but not preferably, the freestanding portion 32 may be omitted. In adepth filter element 12 with more or less than 5 zones 22, the last zone is made as described for the fifth zone 22 above. - Preferably, though not shown in
FIG. 3 , a thin layer of bonding fibers, alternatively called shell or shell-forming fibers, is added over the outermost zone 22 as described in U.S. Pat. Nos. 6,938,781 and 6,986,427. The bonding fibers reduce the appearance of loose filament loops and provide a protective cage on the outer surface of thedepth filter element 12. These bonding fibers may also shrink as they cool, which provides roughness to increase the effective surface area of thedepth filter element 12. - While the Figures are directed to cylindrical filters, the same principles may be applied to a flat sheet or planar product. Such a flat product may be produced along a flat table with the filament sprayers oscillating across the width of the table or by cutting a depth filter element made on a large cylindrical mandrel along its length to obtain a sheet of material.
-
FIG. 4 shows asystem 110 for making a tubular depth filter media continuously to an indefinite length. The media can then be cut into a plurality of individualdepth filter elements 12 of desired length. This system is similar to the system described in U.S. Pat. Nos. 6,938,781 and 6,986,427, for exampleFIG. 5 of U.S. Pat. No. 6,938,781, but with the addition of a filament delivery system to provide an optional fifth zone 22 and a laterally reciprocatingnozzle assembly 117 to produce the Z-filament 30. - The
system 110 includes motor drivenscrew type extruder 112, which is supplied with thermoplastic polymeric material from a source (not shown). Polypropylene is preferred but other materials such as polyesters, Nylon™, or polyurethanes may also be used for some or all of the filaments. Withinextruder 112, the polymeric material is heated to a molten state, at which time it is metered and conveyed intoheated delivery lines 114. The material is conveyed to twofilament delivery systems filament delivery systems -
Filament delivery system 116 includes, for each of fivenozzles displacement metering pump 120 which receives molten polymeric material fromheated delivery line 114 and pumps it toheater block 122. The speed ofmotor 124 which drivesmetering pump 120, and thus the rate at which the material is metered throughpump 120 is electronically controlled by anappropriate controller 126.Motor 124 andcontroller 126 are shown foronly nozzle 127 to simplify the figure, but would typically also be provided one for each ofnozzles - Each
heater block 122, which is independently heated via heating means (not shown), is provided with an internal passage that leads to one ofnozzles heater block 122, is controlled bytemperature control 130. Eachnozzle nozzle nozzles FIG. 4 such thatnozzle 127 has the smallest orifice andnozzle 217 has the largest orifice. - Associated with each
nozzle mechanisms mechanisms nozzles mechanisms - Attenuating
mechanisms optional gas heater 134 andgas supply source 136.Gas supply source 136 provides gas viaconduit 138 and appropriate valves and regulators toheater 134. The temperature ofheater 134 is elevated or lowered to the desired temperature viatemperature control 140. The gas is then fed fromheater 134 throughconduit 142 to attenuatingmechanism 131. Attenuatingmechanisms mechanism mechanism -
Filament delivery system 118 is substantially similar to that ofsystem 116 described above, except thatfilament delivery system 118 delivers a filament so as to actively intermingle with filaments produced by one or more of the nozzles used insystem 116.Filament delivery system 118 has anozzle assembly 117, which includes apolymer extrusion nozzle 144, aheater block 146, and an attenuator 154.Heater block 146 is connected to independently driven positivedisplacement metering pump 148 andmotor 150.Heater block 146 is provided with temperature control 152. Pressurized gas is passed to attenuating mechanism 154 fromgas supply source 156 viaconduit 158. As withdelivery system 116, the attenuator insystem 118 can be associated with an optional gas heater, not shown. The provision of separatefilament delivery systems system 116 andsystem 118. - The
filament delivery system 118 is configured to provide compound motion of thenozzle assembly 117, which produces compound motion of the spray pattern of the filament produced bynozzle 144. In the example shown, attenuator 154 is mounted on abracket 199 such that is can pivot relative toheater block 146. Attenuator 154 is connected to asweep mechanism 198 configured to oscillate the attenuator 154.Nozzle assembly 117 is connected throughheater block 146 to a laterally (side to side relative to mandrel 176)reciprocating mechanism 406. Other means of providing compound motion could also be used. For example, one alternative is to use a pivotingheater block 146 and anozzle 144 and attenuator 154. However, it would be more difficult to rapidly pivot theheater block 146 than the attenuator 154 due to the greater mass of theheater block 146. In another alternative, the laterally reciprocatingmechanism 406 could be replaced with a pivoting mechanism having a distant pivot point such that thenozzle assembly 117 moves back and forth through an arc rather than translates. In general, the motion of thenozzle assembly 117 does not need to be only lateral, but could also include one or more of movement up and down relative tomandrel 176, movement towards or away frommandrel 176, and rotation through an angle relative to mandrel 176, in addition to movement from side to side relative to the length ofmandrel 176. -
Delivery systems patterns nozzles mechanisms filament collection device 174. There is preferably some overlap inadjacent filament patterns filament pattern 221 overlaps with at least half ofpattern 220, optionally at least 85% ofpattern 220 or all ofpattern 220, and possibly also part ofpattern 170.Filament collection device 174 includes central,rotatable collection device 176, alternatively called a mandrel, which extends fromdrive motor 178.Press roller 180, which rotates aboutaxle shaft 181, is disposed adjacent to mandrel 176 and spaced therefrom. The completedfilter element 12 is removed from the open end ofcollection device 176, which is not visible but would be at the left side of thecollection device 176 shown inFIG. 4 . - During operation, the essentially continuous polymer filaments of
streams rotating mandrel 176 and collected thereon. Whilemandrel 176 is shown, it is contemplated that other collection devices may also be used, such as large diameter drums. Simultaneously, an essentially continuous filament or fiber stream is directed according tocompound filament pattern 172, which spans generally between afar edge 182 ofstream 166 and afar edge 184 ofstream 221 and traverses the layers of filaments laid down bystreams Rotating press roller 180 engages the filaments that have accumulated onrotating mandrel 176. As sufficient filaments are built up onmandrel 176,press roller 180 forces non-woven filament mass orfiber structure 186 off the axial (open) end ofmandrel 176 in the direction ofarrow 188 to produce acontinuous filament mass 186 of indefinite length.Filament mass 186 is cut in segments to produceelements 12.Filament mass 186 has a radial dimension, a longitudinal dimension, and a circumferential dimension. The entirefilament collection device 174 may be similar to that described in U.S. Pat. No. 4,240,864 by Lin, the disclosure of which is incorporated herein by reference. -
Nozzles common axis 190, which is preferably about 0-15 degrees offset from parallel tomandrel 176. Eachnozzle axis Axes axis 190 and about 0-15 degrees offset from perpendicular tomandrel 176.Axes filament patterns mandrel 176.Filament pattern 221 is preferably angled inwards, towardsfilament pattern 170, to assist in providing an overlap offilament pattern 221 withfilament pattern 220 andoptionally filament pattern 170.Filament pattern 221 is preferably angled by anglingnozzle 217 inwards. Optionally,attenuator 219 can also be angled inwards. - As a non-limiting example, polymer filaments of
filament patterns mandrel 176 may rotate at between 200 and 600 rpm. -
Compound filament pattern 172 comprisesattenuated pattern 172A,high frequency pattern 172B andlow frequency pattern 172C.Attenuated pattern 172A is generally conical pattern generated by the somewhat random movement of the filament as it is blown by air jets from the attenuator 154.High frequency pattern 172B is created by pivotingattenuated pattern 172A so that is sweeps across a distance of about 50% to 85% of the distance between the primary pattern edges 182 and 184 at themandrel 176. The entirehigh frequency pattern 172B moves from side to side according tolow frequency pattern 172C to create the entirecompound filament pattern 172, which generally covers the entire distance betweenedges mandrel 176.Compound filament pattern 172 originates from anozzle assembly 117 located in a position above or belowpress roll 180 so thatcompound filament pattern 172 travels fromnozzle 144 tomandrel 176 and lands on the formingfilament mass 186 without spraying directly ontopress roller 180. - Servo driven
sweep mechanism 198 causes attenuating mechanism 154 to sweep back and forth through an angle so that theattenuated pattern 172A traverses back and forth along a longitudinal dimension offilament mass 186 according tohigh frequency pattern 172B. Aspattern 172A traverses two or more offiber patterns - In a preferred embodiment,
sweep mechanism 198 comprises a servo drive motor with a cam and follower mechanism. Other suitable devices, such as AC/DC driven mechanical cranks and push rod mechanisms, for example, are also acceptable. In a preferred embodiment,sweep mechanism 198 runs at about 800 to 1200 oscillations per minute while themandrel 176 rotates at 200 to 600, preferably 240 to 400, revolutions per minute (RPM). -
Sweep mechanism 198 is mounted onheater block 146, which also functions as a base for thenozzle 144 and attenuator 154.Heater block 146 is attached tocarriage 408 which is mounted to, and slides on,track 400.Track 400 is preferably generally parallel tomandrel 176.Pneumatic cylinder 402 translatesheater block 146 back and forth alongtrack 400, for example at about 1 to 20 oscillations per minute. Optionally,heater block 146 may be angled to pointnozzle 144 towardspattern edge 184 by up to 45 degrees. Optionally,pneumatic cylinder 402 may be operated such that thenozzle 144 dwells at its left most position, for example for 1-3 seconds, before moving back to the right. Dwell at the right most position, if any, is preferably less than 0.5 seconds. When moving between its end points, thenozzle assembly 117 has a generally constant velocity. Optionally thenozzle assembly 117 may be reciprocated by a servo or other mechanism, and it may have non-linear motion. In another options, the nozzle assembly may swing through an arc rather than moving laterally. - Preferably, the fiber of
compound filament pattern 172 is still relatively liquid when it contacts the fibers offilament patterns compound filament pattern 172, it instantaneously adheres to the fibers offilament patterns compound filament pattern 172 is required to avoid melting of the fibers offilament patterns - As a non-limiting example, polymer filaments of
compound filament pattern 172 are produced in the depth filter of the instant invention by passing polypropylene heated to a temperature of between about 280 degrees C. and about 400 degrees C. through a nozzle having an orifice size of about 0.016 inch at a rate of about 8 pounds per hour and passing at an ambient gas at a temperature of about 25 degrees C. at a rate of about 7 standard cubic feet per minute over the molten polymer stream exiting the nozzle orifice. Other suitable parameter combinations may also be used. - An accumulated mass of
filaments 186 is produced onmandrel 176. In one embodiment,press roller 180 is oriented at an angle relative to mandrel 176 withnip 200 in contact withmandrel 176. As a non-limiting example,outer surface 202 ofpress roller 180 is angularly displaced by about 1 to 10 degrees relative tomandrel 176. In one embodiment, nip 200 contacts mandrel 176 close to edge 182 offilament pattern 166. Because of the angular placement ofpress roller 180, compression of filaments incollective filament mass 186 varies along the length ofpress roller 180. This results in a filament mass having a varying density gradient in the radial dimension, with the filament density offilament pattern 166 being generally greater than that of the filament masses comprised of outer filament patterns. - Fibers from
filament patterns mandrel 176 to build upfilament mass 186 composed of many layers of fibers. These fibers can be described as being laid down in an X-Y plane, or in the longitudinal and circumferential (or latitudinal) dimensions. As the fibers are built up, layer upon layer, they produce a radial or depth dimension.Compound filament pattern 172, combined with the rotation ofmandrel 176, causes the fibers coming fromnozzle 144 to integrate intomass 186 as a “z” direction fiber, extending radially through the zones produced byfilament patterns Filament patterns FIG. 3 . Z-filament 30 ofFIG. 3 is produced bycompound filament pattern 172. Z-filament 30 is preferably placed in a continuous manner from the inside to the outside and back to the inside of 2 or more of the zones 22 during approximately 120 degrees or less of rotation of thedepth filter element 12 and over all of the zones 22 during approximately 10 or more rotations (3600 degrees or more of rotation) of thedepth filter element 12. -
System 110 preferably further includesfilament delivery system 214 which is substantially similar to that ofsystem 116 described above, except thatfilament delivery system 214 preferably includes a means of delivering the filaments in such a manner that they intermingle with filaments produced by one or more of the nozzles used insystem 116.Filament delivery system 214 may include one or more polymer extrusion nozzles. One embodiment uses onenozzle 224 withattenuator 226, positioned at an acute angle relative to mandrel 176 to deliver a filament pattern or stream 228 which contacts filamentmass 186 in a pattern which intermingles with at least some offilament patterns filament pattern 172. - Specifically,
system 214 includesheater block 230, independently driven positivedisplacement metering pump 232 andmotor 234.Heater block 230 is provided withnozzle 224 andtemperature control 236.System 214 is also provided withattenuating mechanism 226 associated withnozzle 224. Pressurized gas is passed to attenuatingmechanism 226 fromgas supply source 238 viaconduit 240. As withdelivery system 116,attenuators 226 can be associated with an optional gas heater, not shown. The provision of separatefilament delivery systems system filament delivery systems traverse filament mass 186 in a radial, or z, dimension. In one embodiment, the source of material forfilament delivery system 214 is extruder 112 viadelivery line 114; in another embodiment, the material source forsystem 214 is separate to provide alternate materials to those used infilament delivery systems -
Delivery system 214 produces a stream of a discrete, essentially continuous polymer filament that is distributed in flaredpattern 228 and directed fromnozzle 224 and attenuatingmechanism 226 towardfilament collection device 174. During operation, thefilament pattern 228 is directed in a flared pattern towardrotating mandrel 176. In one embodiment,filament pattern 228 spans the distance between afar edge 182 ofstream 166 and afar edge 184 ofstream 221. In an alternative embodiment,filament pattern 228 does not span the distance betweenfar edges filament mass 186, e.g., the distance covered byfilament pattern 228 is greater than the distance covered by eachprimary filament stream filament pattern 228 is greater than the distance covered by two or more adjacent primary filament streams 166, 168, 170, 220 and 221. In one embodiment,nozzle 224 is placed at an acute angle of about 10 degrees to about 20 degrees relative tomandrel 176. Static filament 28 inFIG. 3 corresponds with the filament ofspray pattern 228. - Shell-forming
filament delivery system 222 is substantially similar tosystem 116 described above, except that shell-formingfilament delivery system 222 is preferably configured and positioned to produce a relatively smooth outer shell zone on the exterior cylindrical surface offilament mass 186. Shell-formingfilament delivery system 222 preferably uses a different location, polymer throughput rate, and air attenuation setting relative tofilament delivery system 116. Compared tosystem 116,nozzle 244 is preferably placed closer tomandrel 176 and uses a lower polymer throughput rate; additionally, attenuatingmechanism 246 uses less air attenuation. Similar tosystem 116, shell-formingfilament delivery system 222 includesheater block 248,metering pump 250,motor 252,temperature control 254,gas supply source 256, andconduit 258. As a non-limiting example, polymer filaments of filament pattern 262 is produced by extruding polypropylene heated to a temperature of between about 240 degrees C. and about 325 degrees C. throughnozzle 244 having an orifice size of about 0.016 inch at a rate of about 1 pound per hour and passing an ambient gas at a temperature of about 25 degrees C. at a rate of about 1.5 standard cubic feet per minute over the molten polymer stream exiting the nozzle orifice. -
Nozzle 244 is preferably placed so that the filament produced thereby is deposited on the outer zone 22 e formed byfilament pattern 221. This configuration produces a very shallow zone or shell with significant fiber-to-fiber bonding, including some bonding between the fibers of the shell and the fibers of outer zone 22 e. The fiber-to-fiber bonding of the shell essentially eliminates the presence of loose fibers on the surface of the finisheddepth filter element 12 and significantly increases the surface area of the resultingdepth filter element 12. - A sample element was made with a Z-filament nozzle assembly having compound motion. The element had a 3 inch (76 mm) inside diameter and 6.5 inch (165 mm) outer diameter. The element had 5 concentric zones produced by 5 fixed nozzles that collectively produced a 22 inch (560 mm) wide spray pattern. The Z-filament nozzle had an attenuator that produced a spray pattern about 10-15 degrees wide. The Z-filament attenuator oscillated at a rate of 1200 cycles per minute. The mandrel rotated at 400 revolutions per minute. The oscillations of the Z-filament attenautor produced a spray pattern that is about 16 inches (410 mm) wide at the mandrel. The Z-filament nozzle is mounted to a heater block that is angled towards the free end of the mandrel (to the left in
FIG. 4 ) but displaced away from the free end of the mandrel such that the nozzle is still aimed at about the center of the fixed nozzle spray pattern. The nozzle assembly reciprocates through a distance of about 6 inches (150 mm) at a rate of about 5.5 to 6 cycles per minute. The nozzle assembly dwells for about 1 to 2 seconds at the side of its travel closest to the free end of the mandrel. - Alternative elements of the same inside and outside diameter and total filament mass were made a) by oscillating the Z-filament attenuator but without reciprocating the Z-filament nozzle assembly, which was fixed at about the middle of its range of motion and b) by reciprocating the Z-filament nozzle assembly but not oscillating the Z-filament attenuator nozzle.
- The sample element, with compound nozzle assembly motion, and the alternative elements were tested under essentially identical conditions. There were no visual signs of crushing or other deformation of the element, and no signs of crushing demonstrated by changes in filtrate turbidity, throughout the lifetime of the sample element. However, both of the alternative elements had visual signs of crushing and increased filtrate turbidity towards the ends of their lifetimes. The first alternative element, with attenuator oscillation only, had a lifetime only 40% as long as the sample element, and only 52% of the dirt holding capacity of the sample element. The second alternative element, with nozzle assembly translation only, had a lifetime 55% as long as the sample element, and 75% of the dirt holding capacity of the sample element.
- In another example two smaller sample elements were made with a Z-filament nozzle assembly having compound motion. These elements had a 1 inch (25 mm) inside diameter and 2.5 inch (64 mm) outer diameter. The elements had 4 concentric zones produced by 4 fixed nozzles. The Z-filament nozzle oscillated and reciprocated generally as described above. In one sample a wide angle of oscillation was used and in the other sample a narrow angle of oscillation was used. An alternative element of the same inside and outside diameter and total filament mass was made by oscillating the Z-filament attenuator but without reciprocating the Z-filament nozzle assembly. The sample elements made with compound nozzle assembly motion and the alternative elements were tested under essentially identical conditions. The alternative element has a lifetime of 61 minutes.
- The sample element with narrow angle of oscillation hade a lifetime of 68 minutes. The sample element with wide angle of oscillation hade a lifetime of 82 minutes. U.S. Pat. Nos. 6,358,417; 6,916,395; 6,938,781; and, 6,986,427 are incorporated herein by reference. International Publication Number WO 2012034028 is incorporated herein by reference. International Application Number PCT/CA2014064125 is incorporated herein by reference.
- One or more embodiments of the invention have been described in this detailed description with reference to the drawings to help disclose the invention and enable the invention to be practiced. However, the invention is defined by the claims and it is not intended to limit the claims to these specific examples or embodiments. The claims may include alternatives, modifications and equivalents.
Claims (13)
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US201715549446A | 2017-08-08 | 2017-08-08 | |
US17/587,519 US20220152535A1 (en) | 2015-04-28 | 2022-01-28 | Melt-blown depth filter element and method of making it |
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US15/549,446 Division US11266936B2 (en) | 2015-04-28 | 2016-04-01 | Melt-blown depth filter element, method and machine of making it |
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2016
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- 2016-04-01 CA CA2976014A patent/CA2976014A1/en active Pending
- 2016-04-01 JP JP2017550937A patent/JP2018519987A/en active Pending
- 2016-04-01 WO PCT/US2016/025758 patent/WO2016175982A1/en active Application Filing
- 2016-04-01 CN CN201680019986.4A patent/CN107405554B/en active Active
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2022
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Also Published As
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WO2016175982A1 (en) | 2016-11-03 |
CN107405554A (en) | 2017-11-28 |
EP3288663A1 (en) | 2018-03-07 |
US11266936B2 (en) | 2022-03-08 |
US20180028954A1 (en) | 2018-02-01 |
CN107405554B (en) | 2020-11-27 |
JP2018519987A (en) | 2018-07-26 |
CA2976014A1 (en) | 2016-11-03 |
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